We can still prune though we might have nothing to evict

Signed-off-by: Finn Carroll <[email protected]>

server/src/main/java/org/opensearch/index/store/remote/utils/TransferManager.java

@@ -99,6 +99,7 @@ private static FileCachedIndexInput createIndexInput(FileCache fileCache, Stream
             // This local file cache is ref counted and may not strictly enforce configured capacity.
             // If we find available capacity is exceeded, deny further BlobFetchRequests.
             if (fileCache.capacity() < fileCache.usage().usage() + request.getBlobLength() && !fileCache.canOverflow()) {
+                fileCache.prune();
                 throw new IOException("Local file cache capacity exceeded - BlobFetchRequest failed: " + request.getFilePath());
             }
             if (Files.exists(request.getFilePath()) == false) {